Quality Attributes of Yoghurt As Influenced By the Addition of Carrot Juice

Abstract

This study was conducted to evaluate quality attributes of set and stirred yoghurt, mixed with different levels of carrot juice; namely, 0% (plain yoghurt), 5%, 10% and 15% w/w and stored refrigerated for up to 10 days. Yoghurts were produced from fresh cow's milk, skimmed milk powder and a starter culture mixed and incubated at 45oC for 5 hours. The stirred carrot yoghurt was prepared by stirring the carrot juice portions with yoghurt after fermentation, while the set type was produced by mixing the prescribed carrot juice levels with milk before fermentation process. The physicochemical, micro-biological and sensory properties of yoghurt samples were investigated during refrigerated storage at 4±2oC up to 10 days. Addition of carrot juice resulted in significant (P<0.05) decrease in total solid, protein, fat and ash content of yoghurt. Among the different carrot juice levels, the pH values of stirred and set yoghurt samples deceased significantly (P<0.05) with increase in storage period, while titratable acidity increased with the increase in storage period. Degree of syneresis in stirred carrot yoghurt increased slightly as storage time increased, while a reasonable decrease was detected in set carrot yoghurt during storage. Microbiological examination for stirred and set yoghurt sample showed that, within each treatment, lactic acid bacteria count increased with the increase in storage period. On the other hand, within each storage period lactic acid bacteria count decreased with the increase in carrot juice level up to 10%. Generally, carrot juice addition did not show noticeable effect on the survival and activity of lactic acid bacteria. The yeast and moulds count showed no growth for all the examined samples up to day 5, while on the last day of storage (day 10), 9 colonies of total coliform were counted in plain yoghurt samples (0% carrot juice), whereas the other treated yoghurt samples show no growth. Organoleptically, the panelists ranked plain yoghurt (0% carrot juice) superior to that with different levels of carrot juice. And they ranked yoghurt with different carrot juice levels in the following preference order 10%, 15% and 5%. In corporation of carrot juice up to 10% improved some of yoghurt characteristics. Addition of carrot juice did not markedly affect the viability of lactic acid bacteria. Moreover, the carrot juice showed an inhibitory activity against some micro-organisms. Yet, there is a need for further research to make the product more acceptable to the consumer